The two components are connected in series so that the varying resistance in the sender will affect the position of the needle on the gauge.
Printed circuits are plastic sheets on which copper tracks have been printed. Components are plugged directly into the tracks. A few modern cars have flexible printed circuits. The copper tracks are printed in ribbons of flexible plastic, which replace the whole wiring system.
This type of circuit is called an earth-return system any part of it connected to the car body is said to be earthed.
The fuse box is often located in a cluster of components, as illustrated here. The box is shown with the cover off.